1. Field of the Invention
The present invention relates to a method of determining the thickness of an article by employing a noncontacting means and associated apparatus; and more specifically, it relates to such a system for determining wall thickness of transparent articles or portions of articles.
2. Description of the Prior Art
There are a number of known systems for measuring the thickness of transparent objects. These can be divided into two categories, (a) those that contact the object such as capacitive sensors, and (b) those that are noncontacting that measure reflection, scattering, or absorption of radiation. Noncontact techniques have been developed for measuring objects that have well-defined relationships of the inner and outer surfaces such as the cylindrical and coaxial surfaces of drawn glass tubing, some molded containers, and the parallel surfaces of plate glass, for example. For accurately measuring the thickness of irregular objects such as most molded containers, available techniques have been limited.
U.S. Pat. No. 5,636,027 discloses a noncontacting thickness measurement apparatus wherein reflected light is measured by sensing means in order to determine thickness of object made of transparent material. Beam splitters are also employed. See also U.S. Pat. No. 4,902,902.
U.S. Pat. No. 5,291,271 is directed toward measurement of wall thickness of a transparent container employing laser light and sensors receiving light reflected from the surface of the container at a first point and refracted into the container emerging at a second point with a view toward determining thickness.
U.S. Pat. No. 4,822,171 shows a noncontact method to measure wall thickness of a transparent article by projecting a narrow band of light in a longitudinal direction employing sensors that receive light reflected from the surface of the article and refracted into the container emerging at a second portion of the article.
In spite of the foregoing known systems, there remains a need for providing an improved means for measuring the thickness of transparent articles.